May 1, 2012 -- For postmenopausal women who are overweight or obese, new research offers more incentive to start shedding pounds.

According to a study published in the journal
Cancer Research, losing even a small proportion of your overall body weight significantly reduces inflammation in your body and potentially lowers your risk of developing several different types of cancer, including breast cancer.

"I think the main issue is body fat," researcher Anne McTiernan, MD, PhD, director of the Prevention Center at the Fred Hutchinson Cancer Research Center in Seattle, writes in an email to WebMD. "The more fat one has, the more inflammation-producing cells there are, and therefore the more inflammation ... produced and sent into the bloodstream."

Reducing Pounds, Inflammation

For the year-long study, McTiernan and her colleagues recruited 439 women throughout the greater Seattle area who were between the ages of 50 and 75. All of them had a body mass index (BMI) of 25 or higher, which meant that they were all considered overweight or obese. They were otherwise considered healthy, with no history of breast cancer, heart disease, diabetes, or other serious illness. None of them were smokers or heavy drinkers.

The women were split into four groups. The first group dieted, eating between 1,200 and 2,000 calories a day, of which less than 30% were fat calories. The second group exercised 225 minutes per week, both at home and under supervision at a gym. The third group both dieted and exercised. The fourth, the comparison group, did not change either their diet or exercise habits.

After a year, the first and third groups had lost an average of 8.5% and 10.8% of their body weight, respectively. Their reductions in inflammation were even more dramatic.

For example, C-reactive protein levels -- elevated levels of which have been associated with lung and colon cancer -- dropped by an average of 36.1% for the diet group and 41.7% for the diet and exercise group. Other inflammatory indicators dropped as well.

For Weight Loss, Dieting Is Essential

The key to this study's result, says McTiernan, was diet, especially when combined with exercise. "Very few people can lose significant amounts of weight from exercise alone. We've done several year-long studies testing exercise alone, even large amounts up to an hour a day, and on average it produces about 3 to 4 pounds of weight loss over the year," she says. "That being said, our strongest effects were primarily in the combined diet and exercise program."

Obesity and Cancer

For Mitchell Roslin, MD, who was not involved in the research, the study is more evidence that obesity is an inflammatory disease.

"This will become a hot topic," says Roslin, chief of bariatric surgery at Lenox Hill Hospital in New York. "Obesity and cancer is a very interesting angle, which we are just beginning to understand. We don't know what is driving the inflammatory state of obesity, but we know it decreases when you lose weight."

Cancer prevention researcher Kerri Winters-Stone, PhD, says the study is very impressive, especially compared to smaller studies that came before.

"It gives us a better idea of what we can expect at a population level," says Winters-Stone, of the Knight Cancer Institute at Oregon Health and Science University in Portland. "And it gives more evidence of what results from behavioral changes. Diet-induced weight loss is really central to reducing inflammation markers. And these were not extreme weight loss plans. The weight loss came from realistic plans that people can achieve over a year."

Plan to Lose Weight

McTiernan advises women who are overweight to start exercising, to pay close attention to what and how much they eat, and to keep track of progress to help reach a weight loss goal of 1 to 2 pounds per week. She hopes that women will get help to do this from their doctors.